Data transmission to home or business computers typically occurs over two types of telephone lines. The first is an analog telephone line and the second is an ISDN telephone line. In order to transmit or receive data from either of these two lines, one is required to use an apparatus that will modulate or demodulate data between a digital data stream and the telephone line, either ISDN or analog. Currently, for analog lines this is done using an analog modem and for ISDN lines it is done using an ISDN modem.
Unfortunately, analog and ISDN lines require separate modems which are not compatible with the data transmission characteristics of both of these transmission lines. More specifically, an ISDN modem cannot be used with regular analog telephone lines. Similarly, an analog modem cannot be used with ISDN telephone lines. This incompatibility between ISDN lines and telephone lines requires an end user to have additional hardware in order to transmit and receive data over these two different transmission lines, requiring additional expense. Furthermore, the use of both systems together is detrimental to the noise characteristics of the incoming and outgoing signals.